U.S. patent application number 15/267673 was filed with the patent office on 2018-03-22 for method for relieving residual stress in cast-in-place liners of hpdc engine blocks.
The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Maurice G. Meyer, Qigui Wang, Jianghuai Yang.
Application Number | 20180080107 15/267673 |
Document ID | / |
Family ID | 61302450 |
Filed Date | 2018-03-22 |
United States Patent
Application |
20180080107 |
Kind Code |
A1 |
Meyer; Maurice G. ; et
al. |
March 22, 2018 |
METHOD FOR RELIEVING RESIDUAL STRESS IN CAST-IN-PLACE LINERS OF
HPDC ENGINE BLOCKS
Abstract
A method for relieving residual stress in cast-in-place liners
of high pressure die cast (HPDC) engine blocks to prevent cracking
in the liners during the machining process. The method includes
locally heating up the liners and the surrounding engine block
material through rapid induction heating and then cooling down the
liners and surrounding engine block material with still ambient air
to a predetermined temperature after the residual stress has been
reduced to a desired threshold.
Inventors: |
Meyer; Maurice G.; (Fenton,
MI) ; Wang; Qigui; (Rochester Hills, MI) ;
Yang; Jianghuai; (Rochester Hills, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Family ID: |
61302450 |
Appl. No.: |
15/267673 |
Filed: |
September 16, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 6/06 20130101; C21D
1/613 20130101; Y02P 10/253 20151101; C22F 1/04 20130101; C21D 1/42
20130101; F02F 1/18 20130101; Y02P 10/25 20151101; F02F 2200/06
20130101; H05B 6/38 20130101; H05B 6/101 20130101; F02F 1/004
20130101; C21D 1/30 20130101; F02F 7/0085 20130101 |
International
Class: |
C22F 1/04 20060101
C22F001/04; F02F 1/00 20060101 F02F001/00; H05B 6/10 20060101
H05B006/10; H05B 6/06 20060101 H05B006/06; C21D 1/42 20060101
C21D001/42; C21D 1/30 20060101 C21D001/30; C21D 1/613 20060101
C21D001/613 |
Claims
1. A method of relieving residual stress in at least one
cast-in-place liner of a high pressure die cast engine before
machining comprising: calculating a temperature profile of at least
one liner and engine block material surrounding the at least one
liner based on material thermoplastic and mechanical properties;
inductively heating the at least one liner and engine block
material surrounding the at least one liner; controlling the
inductive heating to obtain the calculated temperature profile of
the at least one liner and engine block material surrounding the at
least one liner; and uniformly cooling the at least one liner and
engine block material surrounding the at least one liner to a
predetermined temperature when a relaxed residual stress is less
than or equal to a predetermined relaxed residual stress
threshold.
2. The method of claim 1 wherein inductively heating further
comprises controlling the inductive heating through at least one
adjustable heating path.
3. The method of claim 1 further comprising calculating a residual
stress relaxation of the at least one liner and the engine block
material surrounding the at least one liner in response to the
inductive heating.
4. The method of claim 1 wherein controlling inductive heating
further comprises calculating a heating up rate of the at least one
liner and engine block material surrounding the at least one liner
based on the calculated temperature profile.
5. The method of claim 1 further comprising measuring the relaxed
residual stress of the at least one liner and engine block material
surrounding the at least one liner.
6. The method of claim 2 further comprising determining the at
least one adjustable heating path based on an as cast residual
stress distribution of the at least one liner and the engine block
material surrounding the at least one liner.
7. A method of relieving residual stress in at least one
cast-in-place liner of a high pressure die cast engine before
machining comprising: calculating an as-cast residual stress
distribution of the at least one and engine block material
surrounding the at least one cast-in-place liner; calculating a
heating up rate and a temperature profile of the at least one liner
and engine block material surrounding the at least one liner based
on material thermoplastic and mechanical properties; controlling
inductive heating of the at least one liner and engine block
material surrounding the at least one liner based on the heating up
rate and the temperature profile; measuring a relaxed residual
stress of the at least one liner and engine block material
surrounding the at least liner; and uniformly cooling the at least
one and engine block material surrounding the at least one liner to
a predetermined temperature when the measured relaxed residual
stress is less than or equal to the predetermined relaxed residual
stress threshold.
8. The method of claim 7 wherein controlling inductive heating
further comprises controlling inductive heating through at least
one adjustable heating path based on the as-cast residual stress
distribution of the at least one liner and engine block material
surrounding the at least one liner.
9. The method of claim 7 wherein uniformly cooling further
comprises cooling the at least one and engine block material
surrounding the at least one liner in still ambient air.
10. The method of claim 7 wherein uniformly cooling further
comprises cooling the at least one and engine block material
surrounding the at least one liner in forced warm air.
11. The method of claim 7 wherein uniformly cooling further
comprises cooling the at least one and engine block material
surrounding the at least one liner by water mist quenching.
Description
FIELD
[0001] Apparatuses consistent with exemplary embodiments relate to
a method for relieving residual stress in high pressure die cast
(HPDC) engine blocks before machining. More particularly,
apparatuses consistent with exemplary embodiments relate to a
method for relieving residual stress in cast-in-place liners of
high pressure die cast (HPDC) engine blocks.
BACKGROUND
[0002] Because of rapid cooling and particularly non-uniform
cooling in the high pressure die casting process, a significant
amount of residual stress can be developed in HPDC engine parts.
With cast-in-place liners, even more residual stress is produced in
the liners and surrounding aluminum.
[0003] High stresses in the liners at the interbore areas can cause
cracking during post-cast machining and durability testing.
Conventional lower temperature ageing heat treatment post HPDC to
strengthen the aluminum alloy blocks has proven to produce little
effect of relieving the cast residual stress. In some cases, liners
made from high strength/high durability materials are used to avoid
the cracking and fracturing that frequently occurs during machining
or testing as a result of residual stresses in the parts after the
HPDC process.
[0004] It is appreciated that the use of high strength/high
durability materials is effective in mitigating the issues
resulting from residual stresses affecting cast-in-place liners
after the HPDC engine process, this approach is known to be costly,
harder to machine, and can reduce fuel efficiency due to increased
material weight. As such, aspects of the following exemplary method
provides an alternative approach that addresses the issues
associated with post-HPDC residual stresses while avoiding the
concerns that arise with using high strength/high durability
material liners.
SUMMARY
[0005] One or more exemplary embodiments address the above issue by
providing a method for relieving residual stress in high pressure
die cast (HPDC) engine blocks. More particularly, apparatuses
consistent with exemplary embodiments relate to a method for
relieving residual stress in cast-in-place liners of high pressure
die cast (HPDC) engine blocks before machining. According to an
aspect of an exemplary embodiment, a method of relieving residual
stress in a cast-in-place liner of a high pressure die cast engine
before machining includes calculating a temperature profile of at
least one liner and engine block material surrounding the at least
one liner based on material thermoplastic and mechanical
properties.
[0006] Further aspects include inductively heating the at least one
liner and engine block material surrounding the at least one liner,
and controlling the inductive heating to obtain the calculated
temperature profile of the at least one liner and engine block
material surrounding the at least one liner. Another aspect of the
exemplary embodiment includes uniformly cooling the at least one
liner and engine block material surrounding the at least one liner
to a predetermined temperature when a relaxed residual stress is
less than or equal to a predetermined relaxed residual stress
threshold.
[0007] Still further aspects include controlling the inductive
heating through at least one adjustable heating path, and
calculating a residual stress relaxation of the at least one liner
and the engine block material surrounding the at least one liner in
response to the inductive heating. Yet another aspect of the
exemplary embodiment includes calculating a heating up rate of the
at least one liner and the block material surrounding the at least
one liner based on the calculated temperature profile. Still
another aspect includes measuring the relaxed residual stress of
the at least one liner and the engine block material surrounding
the at least one liner.
[0008] Another aspect of the exemplary embodiment includes
determining the at least one adjustable heating path based on an
as-cast residual stress distribution of the at least one liner and
the engine block material surrounding the at least one liner.
[0009] Other objects, advantages and novel features of the
exemplary embodiments will become more apparent from the following
detailed description of exemplary embodiments and the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will be better understood from the
description as set forth hereinafter, with reference to the
accompanying drawings, in which:
[0011] FIG. 1 is an illustration of an open deck high pressure die
cast (HPDC) engine block including cast-in-place liners in
accordance with an exemplary embodiment;
[0012] FIG. 2A is an illustration of an inductive heating apparatus
positioned for heating the cast-in-place liners of the HPDC engine
block in accordance with an exemplary embodiment;
[0013] FIG. 2B is an illustration of a muted view of a plurality of
adjustable-path heating coils arranged within the cast-in-place
liners in accordance with an exemplary embodiment;
[0014] FIG. 3 an illustration of schematic view of the central
control system, the heating control units, and the adjustable-path
heating coils of the inductive heating apparatus in accordance with
the exemplary embodiment; and
[0015] FIG. 4 is an illustration of a flow diagram of an algorithm
for relieving residual stress in cast-in-place liners of (HPDC)
engine blocks.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The following description is merely exemplary in nature and
is not intended to limit the present disclosure, application, or
uses. FIG. 1 provides an illustration of an open deck HPDC engine
block 102 including cast-in-place liners 104 with engine block
material 106 surrounding the cast-in-place liners 104 in accordance
with aspects of an exemplary embodiment. In the exemplary
embodiment, the engine block 102 is made of aluminum (AL) or an
aluminum alloy materials such as, but not limited to, A360, A380,
or A390. The cast-in-place liners 104 may be made from cast iron,
steel, or various cast iron or steel alloys. In the casting
process, the liners 104 are held in place by mandrels at locations
that will form the inside surface of the engine's 102 piston
cylinders. After the molten metal engine block material is poured
and allowed to solidify, the liners become part of the engine
block.
[0017] Residual stress in the liners 104 and engine block material
106 surrounding the liners is developed due to differences in the
respective material's thermal expansion or contraction
coefficients. Roughly, aluminum expands or contracts about 8 times
that of cast iron liners. The differences in the thermal expansion
or contraction coefficients cause uneven temperature distribution
in the HPDC engine 102 during the manufacturing process, primarily
due to the casting and cooling of the different materials used such
as cast iron liners and surrounding aluminum engine block. High
tensile residual stress in the liners 104 can cause cracking and
fractures when the residual stress is greater than liner tensile
strength.
[0018] Referring now to FIG. 2A, an illustration of an inductive
heating apparatus 200 arranged for heating the cast-in-place liners
104 of the HPDC engine block 102 in accordance with an exemplary
embodiment is provided. The inductive heating apparatus 200
includes power signal circuits 210a 210b, 210c, and 210d for
providing a power signal to heating control units 205a, 205b, 205c,
and 205d which controls the inductive heating distribution
(including heating up rate, adjustable heating path, and
temperature profile) in the inductive heating elements 215a, 215b,
215c, and 215d. A central system 225 that is operative to manage,
command, direct and regulate the functions of the inductive heating
apparatus 200 as according to aspects of the exemplary embodiment.
It is appreciated that the central control system 225 can be either
an open or dosed loop system, For an open system, a detailed
calibration needs to be done to optimize the heating up time and
the applied power. For a dosed loop system, emperature sensing
units (not shown) would be employed proximately to the
cast-in-place liners 104 and the engine block material 106
surrounding the liners 104 to provide a real-time temperature
signal back to the heating control units 205a-205d which control
the heating up rate, adjustable heating path, and temperature
profile.
[0019] FIG. 2B provides an illustration of a muted view of a
plurality of adjustable-path heating coils 220a, 22b, 220c, and
220d disposed within the inductive heating elements 215a-215d when
positioned within the cast-in-place liners 104 in accordance with
an exemplary embodiment. It is appreciated that the adjustable-path
heating coos are operative to be selectively controlled by heating
control units 210a-210d to inductively heat any fraction of or
entire body of the cast-in-place liner 104 and engine block
material 106 surrounding the cast-in-place liner 104 as according
to aspects of the exemplary embodiment.
[0020] FIG. 3 is an illustration of schematic view 300 of the
central control system 225, the heating control units 205a-205d,
and the adjustable-path heating coils 305a-305d, 310a-310d,
315a-315d, and 320a-320d of the inductive heating apparatus 200 in
accordance with the exemplary embodiment. As illustrated, each
inductive heating element 215a-215d may consist of a plurality of
adjustable heating coils 220a-220d.
[0021] In the exemplary embodiment, each inductive heating element
215a-215d includes 4 adjustable heating coils 220a-220d wherein
each adjustable heating coil is operative to heat one quarter of
the cast-in-place-liner 104 and the engine block material 106 (not
shown) surrounding the liners 104. The heating up rate, heating
path, and temperature profile of each cast-in-place liner 104 and
engine block material 106 can be adjusted by the central control
system 225 or the respective control units 205a-205d as each coil
is wired separately for independent control.
[0022] Thus, each bore can be variably heated at a desired
temperature, in a sequential manner or at the same time, for
different periods of time, and through independent adjustable
heating paths 220a-220d as according to a temperature profile to be
obtained.
[0023] Referring now to FIG. 4, an illustration of a flow diagram
of an algorithm 400 of the method for relieving residual stress in
cast-in-place liners of (HPDC) engine blocks before machining is
provided. At block 405, the method begins with calculating the
residual stress of the at least one cast-in-place liner 104 and the
engine block material 106 surrounding the liner. This includes
determining the initial temperatures of the melted engine block
material and the casting die to be filled. Thereafter, thermal
analysis is performed on the filling of the mold, the
solidification of the molten material, and the cooling down process
as accomplished by air or liquid quenching. The relevant
calculations for thermal analysis are as follows: During mold
filling, the heat transfer of moving liquid metal can be calculated
using:
.differential. H .differential. t + .gradient. Hv = k .gradient. 2
T , ##EQU00001##
where the enthalpy, H=.intg..rho.c.sub.pdT. During solidification,
the heat transfer of a solidifying aluminum casting follows the
energy equation and can be simplified as:
.differential. ( .rho. C p T ) .differential. t = - .gradient. (
.rho. v C p T ) + .gradient. ( k .gradient. T ) - .rho. L
.differential. f l .differential. t ##EQU00002##
where .rho. is the density (kg/m.sup.3); C.sub.p is the specific
heat (Jkg.sup.-1K.sup.-1); T is the temperature (K); v is the
velocity vector (ms.sup.-1), L is the latent heat (Jkg.sup.-1); and
k is the thermal conductivity (Wm.sup.-1K.sup.-1).
[0024] The thermal analysis results are further used to determine
the nodal residual stress distribution within the at least one
cast-in-place liner 104 and the engine block material 106
surrounding the liner as according to aspects of the exemplary
embodiment.
[0025] At block 410, the method continues with calculating the
stress relaxation of the at least one cast-in-place liner 104 and
the engine block material 106 surrounding the liner in response to
inductive heating. The as-cast residual stress distribution values
are used in a finite element analysis simulation of inductive
heating to determine the stress relaxation of the at least one
cast-in-place liner 104 and the engine block material 106
surrounding the liner. The equations used are as follows as
according to the exemplary embodiment. The total strain, due to
temperature difference in the casting may be determined from
intrinsic strength {circumflex over (.sigma.)}.sub.e, and strain
hardening {circumflex over (.sigma.)}.sub.p.
.sigma. .mu. ( T ) = C e ( . , T ) .sigma. ^ e .mu. 0 + C p ( . , T
) .sigma. ^ p .mu. 0 ##EQU00003##
where C.sub.e({dot over (.epsilon.)},T), and C.sub.p({dot over
(.epsilon.)},T) are velocity-modified temperatures for intrinsic
strength, and strain hardening, respectively; T is the temperature
measured in Kelvin and {dot over (.epsilon.)} is the strain rate;
.mu..sub.0 (=28.815 GPa) is a reference shear modulus value at 0 K
and {dot over (.epsilon.)}=10.sup.7s.sup.-1 for the aluminum
casting; and .mu.(T) is a temperature-dependent shear modulus.
After yield, flow stress may be modeled through evolution of strain
hardening {circumflex over (.sigma.)}.sub.p
.sigma. ^ p = .sigma. ^ p ' + .mu. ( T ) .mu. 0 .theta. 0 [ 1 -
.sigma. ^ p ' .sigma. ^ os ] d ##EQU00004##
where .theta..sub.0 represents the slope of the stress-strain curve
at yield in the reference state (0 K, {dot over
(.epsilon.)}=10.sup.7s.sup.-1) and {circumflex over
(.sigma.)}.sub.OS is a parameter of one of the material
properties.
[0026] At block 415, the method continues with calculating a
temperature profile and heating up rate of the at least one
cast-in-place liner 104 and engine block material 106 surrounding
the at least one liner 104 based on the material thermoplastic and
mechanical properties of the at least one liner 104 and engine
block 102.
[0027] As according to aspects of the exemplary embodiment, the
engine block 102 is formed of aluminum or an aluminum alloy
material and the liner(s) 104 are formed from cast iron. It is
appreciated that these materials have different thermoplastic and
mechanical properties but the temperature profile and heating up
rate are primarily dependent on the engine block material such that
incipient melting or blistering of the material is avoided. For
example, the highest temperature of heating the aluminum engine
block material 106 surrounding the cast iron liners 104 to avoid
melting is between 400-500.degree. C. at a heating up rate of
10-30.degree. C./s while the highest temperature for heating cast
iron before melting is between 1000-1100.degree. C. at the same
rate.
[0028] A slower heating up rate applies to low ductility aluminum
materials, e.g., 10.degree. C./s, and a faster heating up rate
applies for high ductility materials, e.g., 30.degree. C./s,
wherein finite element analysis is used to determine the actual
temperature profile and heating up rate as according to the below
equations: .sigma.=E.alpha..DELTA.T<.sigma.UTS, where .sigma. is
thermal stress, E is Young's modulus, a is linear thermal expansion
coefficient, .DELTA.T is the change in temperature at a given time,
.sigma.UTS is the ultimate tensile strength of the engine block
material. As according to aspects of the exemplary embodiment, a
heating path is adjustable for heating the at least one
cast-in-place liner 104 and engine block material 106 surrounding
the liner to desired stress relaxation levels, particularly at the
as-cast residual stress distribution nodes that are expected to be
susceptible to fracturing/cracking during the machining
process.
[0029] Referring now to block 420, the method continues with
controlling the inductive heating based on the temperature profile,
heating up rate, and heating path as required to obtain the desired
stress relaxation levels in the at least one cast-in-place liner
104 and engine block material 106 surrounding the liner as
according to aspects of the exemplary embodiment. It is appreciated
that heating control is performed by the heating control units
205a-205d and the central control system 225 either by operation of
a closed system that requires a sensing circuit for feedback (not
shown), or open loop system which would require detailed
calibration initially and periodically as part of equipment
maintenance.
[0030] At block 425, the method continues with measuring the
relaxed residual stress in response to inductive heating as
according to an exemplary embodiment. Relaxed residual stress is
measured by a destructive or non-destructive approach, but not
limited to, strain gauge method, hole-drilling, X-ray diffraction,
or neutron diffraction.
[0031] At block 430, the method continues by determining if the
measured relaxed residual stress is less than or equal to a
calculated relaxed residual stress threshold. If it is determined
that the measured relaxed residual stress is less than or equal to
the calculated relaxed stress threshold then the at least one
cast-in-place liner 104 and engine block material 106 surrounding
the liner is uniformly cooled down to a predetermined temperature.
As according to aspects of the exemplary embodiment, the cooling
down process will be naturally done in still ambient air but other
methods such as forced ambient air, or forced warm air to achieve
the predetermined temperature before machining. If the measured
relaxed residual stress is not less than or equal to the calculated
relaxed residual stress then the method returns to block 420 to
further control the inductive heating until the measured relaxed
residual stress is less than or equal to the calculated relaxed
stress threshold.
[0032] The description of the invention is merely exemplary in
nature and variations that do not depart from the gist of the
invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention.
* * * * *